1. Field of the Invention
The present invention relates generally to a method for measuring an offset of a resolver, more particularly to a method for measuring an offset of a resolver, which may frequently measure and correct the offset of the resolver by actively performing zero current control in a motor while a vehicle is driven.
2. Description of the Related Art
A Motor Control Unit (MCU) is used for controlling a motor, such as a synchronous motor or an induction motor, which are used in electric vehicles or hybrid vehicles. In order to control such a motor, the MCU performs calculations for setting coordinates depending on the position of the magnetic flux of the motor. In this case, a resolver is used to detect the absolute position of a rotor of the motor.
A resolver is a type of electronic transformer. When an excitation voltage is applied to a primary winding (input) and a shaft is rotated, a magnetic coupling coefficient changes, and thus a voltage having variable amplitude is generated in a secondary winding (output). This voltage makes the secondary winding be arranged to correspond with the sine and cosine of the rotation angle of the shaft. Therefore, the rotation angle of the resolver may be acquired by determining the ratio of the amplitude of the sine output to the amplitude of the cosine output.
The resolver operated as described above provides the MCU with the rotor position by detecting the velocity and phase of a motor, and the MCU uses the rotor position to generate a torque control command and a speed control command.
Meanwhile, because of various reasons, such as error in assembling a resolver and a motor, an inaccurate position of a coil in the resolver, and the like, an offset may be generated in the output of the resolver, and thus the absolute position of the rotor cannot be accurately measured due to the offset. Accordingly, various methods for measuring and correcting the resolver offset have been proposed.
According to a conventional method for measuring an offset of a resolver, while a vehicle is driven, a mode in which zero current control can be performed is determined, and the offset of a resolver is measured when entering the corresponding mode.
However, according to the conventional method, because the section in which the zero current control can be performed mostly corresponds to a zero torque section and there are few zero torque sections while a vehicle is driven, the frequency of measuring the resolver offset is very low. Also, if the zero torque section is prolonged for measuring the resolver offset, it may adversely affect drivability of the vehicle.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.